I've had a trouble ticket open now for over a week due to version 21 upgrade problems. Like everyone else, the AS module drops out frequently leaving us completely unprotected. Anyway, I got notice in my trouble ticket that version 21.1 is in testing and will release soon. Here's the quotes
Thank you for contacting GFI Support. It was confirmed to be a bug in version 21, causing this and developers team is working on the solution. I\ll inform you in this ticket as sun the working solution will be confirmed from them
to which I replied
I need some kind of ETA from you. I'm now being added to spam lists because Mailessentials 21 is failing and delivering back scatter, and because of this my users emails can longer reach their destinations. This is situation is NOT acceptable.
and received the response today:
We are in process of testing version 21.1 which suppose to fix all issues, and publicly available this week
So fingers crossed, our collective misery may soon be over.